Expected geoneutrino signal at JUNO using local integrated 3-D refined crustal model

Abstract

Geoneutrinos are a unique tool that brings to the surface information about our planet, in particular, its radiogenic power, which, however, can also provide insight into its formation and chemical composition. To date, only the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) and Borexino experiments observed geoneutrinos, with the former characterized by low concentration of heat-producing elements in the Earth in contrast to the latter that sets tight upper limits on the power of a georeactor hypothesized to be present inside the Earth. With respect to the results yielded therefrom, a small discrepancy has been identified. On this account, next generation experiments like Jiangmen Underground Neutrino Observatory (JUNO) are needed if it is to provide definitive results with respect to the Earth’s radiogenic power, and to fully exploit geoneutrinos to better understand the natural radioactivity of our planet. An accurate a priori prediction of the crustal contribution plays an important role in enabling the translation of a particle physics measurement into above geo-scientific questions. The process of building a crustal model also represents the ultimate opportunity for particle physicists and geologists to independently measure and test their predictions of the structure and composition of Earth’s interior. The existing crustal models of JUNO are GIGJ (GOCE Inversion for Geoneutrinos at JUNO) and JULOC (JUno LOCal) model. GIGJ model only focused on constructing a geophysical model of the local crust, lack of local geochemical information. JULOC is a 3-D crustal model with geological, geochemical, and geophysical data. However, due to limitations with respect to data, the model only able to be achieved for the top layer of the upper crust (less than 5 -km), didn’t provide refined geochemical information in vertical depth. Building geochemical distribution in vertical is also a difficulty and attractive points in geo-scientific filed. This paper reports on the development of JUNO’s first 3-D integrated crustal model, JULOC-I, which combines seismic, gravity and rock sample data constrained by thermal flow data and also designs of a new building method, solved the problem of geochemical distribution in vertical depth. JULOC-I estimates the total lithosphere geoneutrino signal to be 44.4+5.1−4.4 TNU (Terrestrial Neutrino Units). Results shows higher than expected geoneutrino signals are mainly attributable to higher uranium (U) and thorium (Th) in southern China than that found elsewhere on Earth. Moreover, the high level of accuracy of the JULOC-I model, complemented by 10 years of experimental data, indicates that JUNO has an opportunity to test different mantle models. Predictions by JULOC-I can be tested after JUNO goes online and higher accuracy local crustal model continue to play an important role to improve mantle measurements precision.